The present invention relates to a spark plug for an internal combustion engine.
German Patent No. 196 23 989 describes a spark plug where a center electrode is inserted into the insulator at the end on the side of the combustion chamber, into a cylindrical, axial bore hole. A metallic contact pin provided with a layer of nickel or of a nickel-silver alloy is arranged downstream, in the direction of the insulator end away from the combustion chamber. This contact pin is in electrical contact with the center electrode.
The spark plug according to the present invention has the advantage that the corrosion resistance of the contact pin is effectively improved using a simple solution. Thus, the spark plug""s operational reliability is improved. Furthermore, it is ensured that the center electrode is stable in retaining its shape and location, thereby preventing an increase in the required ignition voltage.
Therefore, from a standpoint of production engineering, it is favorable to coat the entire surface of the contact pin. It is also advantageous from a standpoint of production engineering to coat using thermal spraying or deposition from the gas phase, in particular using aluminization, thereby enabling the spark plug according to the present invention to be produced in large quantities. Furthermore, it is advantageous that the coated contact pin be pre-oxidized prior to being installed because this forms an A12O3 protective layer. Forming the contact pin from an Fe-Co-Ni alloy is advantageous since the alloy is adjusted to the average coefficient of the insulator""s thermal expansion. In addition, it is advantageous for the contact pin to have a cylindrical shape and a larger diameter at the end away from the combustion chamber, in particular to be step-wise or conically offset, since, in this way, the contact pins can be advantageously transported during manufacturing. Manufacturing the spark plug with a simple cylindrical or conical shape is equally advantageous, since the number of manufacturing steps can be decreased.
A tip of the contact pin that tapers in a conical manner on the side of the combustion chamber is advantageous because a higher pressurization of the end of the contact pin on the side of the combustion chamber can be achieved during production.